1. Field of the Invention
The present invention relates to an ink jet recording apparatus in which recording is performed by ejecting a recording liquid (referred to as ink hereinafter) from ink ejection orifices to fly in the form of droplets, and causing the ink to adhere onto a recording medium.
2. Description of the Related Art
In an ink jet recording system, an image is recorded by ejecting ink droplets from an ink jet recording head to a recording medium such as paper, a high image-quality recording medium (e.g., specific coated paper, calendered paper, or a calendered film), and an OHP film. Therefore, mists may occur due to fine ink droplets generated in addition to the ejected ink droplets, and a rebounding of the ink droplets ejected to impinge against the recording medium. Such mists may deposit on an ejection surface of the ink jet recording head. If a large amount of those ink droplets deposit around ejection orifices, or if foreign matters such as paper dust adhere to the deposited ink droplets, there arise problems of impairing the ink ejection and causing troubles including an undesirable deflection (a deviation of the ink droplets from the desired direction) and an ejection failure.
Particularly, when a gap between the ink jet recording head and the recording medium (referred to a head-to-paper gap hereinafter) is as narrow as not more than 1 mm, a large amount of the rebounding mist deposits around the ejection orifices.
In the ink jet recording system, the above problems are generally coped with by widening the head-to-paper gap to reduce the amount of the ink mists deposited, or wiping the ejection surface with a blade, which is formed of a rubber-like elastic member, to clean and remove the contaminations caused by the ink mists on the ejection surface.
Further, a recording medium which is extensible upon absorbing a large amount of ink, such as ordinary paper, accompanies a problem below. If the gap between the ink jet recording head and the recording medium is narrow, the head scratches the recording medium because the recording medium sags during high-duty recording due to a cockling thereof.
The above problem is also generally coped with by widening the head-to-paper gap. Widening the head-to-paper gap however increases the undesired deflection proportionally, thus resulting in a degradation of recording quality. Moreover, in an ink jet recording apparatus having a plurality of ink jet recording heads for color recording, registration of the heads (head alignment) is more apt to lose accuracy, which degrades recording quality and impairs color balance.
Meanwhile, recording is often made by using not only ink but also a treatment liquid for making a color material in the ink insoluble from the standpoints of improving water resistance and image quality. Although such a method is effective in improving water resistance and image quality, the ink made insoluble is gradually deposited at the orifices and thereabout in the ejection surface due to the aforesaid rebounding mist. Those deposits are hard to remove by the above-described wiping, preliminary ejection, or restoration by suction, and a serious ejection failure may occur.
Deposition of the ink made insoluble at the ejection orifices, etc. occurs primarily based on a phenomenon below. Ink droplets and a treatment liquid both ejected from an ink jet recording head rebound from a recording medium and are then deposited onto the ink jet recording head after being mixed together. Especially, if the ink droplets are ejected to an area to which the treatment liquid has been already ejected, the treatment liquid and the ink droplets may rebound and deposit onto the head in the form of an insoluble resulting from reaction between them.
Japanese Patent Laid-Open No. 9-216354 discloses an invention wherein a cover plate is provided to protect the ejection surface of an ink jet recording head in consideration of the nature and behavior of the rebounding mist generated upon ink and a treatment liquid impinging against a recording medium in an superimposed relation.
With the above related art, however, because the cover plate is provided between the ink jet recording head and the recording medium, the head-to-paper gap must be increased by an amount corresponding to a thickness of the cover plate, and recording quality degrades for the reasons mentioned above.